This is a great piece of history. It is worthy of being a coffee table book for ancient programmers. If you are ancient, it will bring back memories of the good times. If you are a young whippersnapper then this book is necessary to understand what came before you.
In a time when computing power was just a fraction of today's capacity. Someone thought up things like SQL and other exotic solutions to make computing front-ends easier to understand. Then we moved into CASE tools.
Terminology changed and newer concepts were tacked on. If you keep up with the changes, this book is useful to get a different perspective on “The Fusion Method.”
Most people dumped this long ago. We never went back to spaghetti programming which is the most efficient but by using lower-level languages we cut out the overhead of time/space and added flexibility. Still knowing the concept will help you if you run into any of this old code.